The answer is c) a pollen tube grows from the pollen grain into the ovary.
Pollen tube is used to transport pollen from the stigma of a
flower to the ovary. Actually, pollen begins to grow into pollen tube when lands on the stigma. It
grows until it reaches an ovule which is inside the ovary. This way it is secured that
a nucleus of pollen will fuse with a nucleus of the ovule and
that fertilization will occur.
